#include<stdio.h>
int main()
{
	int h1=0,m1=0,h2=0,m2=0;
	scanf("%2d%2d%2d%2d",&h1,&m1,&h2,&m2);
	int h=h2-h1;
	int m=m2-m1;
	if(m<0)
	{
		m+=60;
		h--;
	}
	printf("%02d:%02d",h,m);
	return 0;
}
